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elisp: Kinds of Files

 
 24.6.2 Distinguishing Kinds of Files
 ------------------------------------
 
 This section describes how to distinguish various kinds of files, such
 as directories, symbolic links, and ordinary files.
 
  -- Function: file-symlink-p filename
      If the file FILENAME is a symbolic link, the ‘file-symlink-p’
      function returns its (non-recursive) link target as a string.  (The
      link target string is not necessarily the full absolute file name
      of the target; determining the full file name that the link points
      to is nontrivial, see below.)  If the leading directories of
      FILENAME include symbolic links, this function recursively follows
      them.
 
      If the file FILENAME is not a symbolic link, or does not exist,
      ‘file-symlink-p’ returns ‘nil’.
 
      Here are a few examples of using this function:
 
           (file-symlink-p "not-a-symlink")
                ⇒ nil
           (file-symlink-p "sym-link")
                ⇒ "not-a-symlink"
           (file-symlink-p "sym-link2")
                ⇒ "sym-link"
           (file-symlink-p "/bin")
                ⇒ "/pub/bin"
 
      Note that in the third example, the function returned ‘sym-link’,
      but did not proceed to resolve it, although that file is itself a
      symbolic link.  This is what we meant by “non-recursive” above—the
      process of following the symbolic links does not recurse if the
      link target is itself a link.
 
      The string that this function returns is what is recorded in the
      symbolic link; it may or may not include any leading directories.
      This function does _not_ expand the link target to produce a
      fully-qualified file name, and in particular does not use the
      leading directories, if any, of the FILENAME argument if the link
      target is not an absolute file name.  Here’s an example:
 
           (file-symlink-p "/foo/bar/baz")
                ⇒ "some-file"
 
      Here, although ‘/foo/bar/baz’ was given as a fully-qualified file
      name, the result is not, and in fact does not have any leading
      directories at all.  And since ‘some-file’ might itself be a
      symbolic link, you cannot simply prepend leading directories to it,
      nor even naively use ‘expand-file-name’ (File Name
      Expansion) to produce its absolute file name.
 
      For this reason, this function is seldom useful if you need to
      determine more than just the fact that a file is or isn’t a
      symbolic link.  If you actually need the file name of the link
      target, use ‘file-chase-links’ or ‘file-truename’, described in
      Truenames.
 
    The next two functions recursively follow symbolic links at all
 levels for FILENAME.
 
  -- Function: file-directory-p filename
      This function returns ‘t’ if FILENAME is the name of an existing
      directory, ‘nil’ otherwise.
 
           (file-directory-p "~rms")
                ⇒ t
           (file-directory-p "~rms/lewis/files.texi")
                ⇒ nil
           (file-directory-p "~rms/lewis/no-such-file")
                ⇒ nil
           (file-directory-p "$HOME")
                ⇒ nil
           (file-directory-p
            (substitute-in-file-name "$HOME"))
                ⇒ t
 
  -- Function: file-regular-p filename
      This function returns ‘t’ if the file FILENAME exists and is a
      regular file (not a directory, named pipe, terminal, or other I/O
      device).
 

Info Catalog elisp: Testing Accessibility elisp: Information about Files elisp: Truenames